Save the transformation of Boolean Modifier Difference
Modifiers are what is called non-destructive modifications, they are meant for users to be able to do further editing before committing to a final irreversible transformation.

The idea is that you don't apply a modifier until you need to (if at all). It is not uncommon to never apply the modifiers. That way you can experiment or refine the settings, or further combine it with other modifiers, or change the order in which the modifiers act, without effecting the original object.

If you need to make the modification permanent then Apply the modifier. The transformations will now be part of the object and the modifier will disappear.